Using header window to explore python
As you said you have the right click mouse to select a line, you can select a block of line with B then click and drag for select or middle mouse click and drag for un-select. And you can select and un-select all the line with A. 

You can delete all selected lines by pressing X.

As far as I know, the only way to copy a line is CtrlC. 

My tip for selecting only one line is, if you have other lines selected, do A for un-select all and then copy your line.

Last thing, for navigating you can use the middle mouse wheel but you can also use the middle mouse wheel click then click and drag.